In recent years, multilevel output has becoming a commonly used technology in the field of middle-high voltage high power frequency conversion. The active neutral point clamped multilevel circuit is a commonly used multilevel inverting circuit. In the active neutral point clamped multilevel circuit, at least one floating capacitor is provided at a certain position, such that the level of the circuit is clamped, thereby generating different output levels.
FIG. 1 illustrates a commonly used five-level inverting circuit, which includes multiple switch transistors and freewheel diodes, where the multiple switch transistors are turned on and turned off according to preset logics, thereby implementing inversion. However, the five-level inverting circuit includes three direct current (DC) capacitors. If some of the switch transistors are turned on simultaneously, the DC capacitor may be short circuited, thereby resulting in a great short-circuit current in the loop, thus the switch transistor may be damaged.
Therefore, providing a PWM control method for a five-level inverting circuit in order to prevent the DC capacitor from being short circuited is a major technical issue to be solved by a person skilled in the art.